calcEk.C

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/*======================================================================*/
 
// This routine evaluates q(k) (McComb, p61) by summing all wavevectors
// in a k-shell. Then we divide through by the volume of the box
// - to be accurate, by the volume of the ellipsoid enclosing the
// box (assume cells even in each direction). Finally, multiply the
// q(k) values by k^2 to give the full power spectrum E(k). Integrating
// this over the whole range gives the energy in turbulence.
 
/*======================================================================*/
 
#include "calcEk.H"
#include "fft.H"
#include "Kmesh.H"
#include "kShellIntegration.H"
#include "volFields.H"
#include "graph.H"
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
namespace Foam
{
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
graph calcEk
(
    const volVectorField& U,
    const Kmesh& K
)
{
    label ntot = 1;
    forAll(K.nn(), idim)
    {
        ntot *= K.nn()[idim];
    }
 
    scalar recRootN = 1.0/sqrt(scalar(ntot));
 
    return kShellIntegration
    (
        fft::forwardTransform
        (
            ComplexField(U.primitiveField(), vector::zero),
            K.nn()
        )*recRootN,
        K
    );
}
 
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
} // End namespace Foam
 
// ************************************************************************* //